Impact of pupillary dilation on the efficacy of laser peripheral iridotomy

Purpose: To assess outcomes of laser peripheral iridotomy (LPI) procedures following dilation by evaluating the pressure difference across the iris posterior-anterior chamber resulting from varying hole sizes and locations. Methods: Using an anterior segment optical coherence tomography (AS-OCT) image, we created a 3-D finite element model of the iris. We then manually identified a dilator region where the dilator stress was applied to simulate pupillary dilation. To mimic LPI, we made a hole of 200 microns in diameter near the pupillary margin, at the mid-periphery, and at the periphery of the iris. Using computational fluid dynamics methods, we computed the pressure difference developed by the hole before and after pupil dilation at each location. This process was then repeated with a hole of 400 microns in diameter. Results: The pressure difference developed across a 200-micron hole when the hole was placed near the pupil, at the iris mid-periphery, and near the iris periphery was 0.85 Pa, 0.80 Pa, and 0.92 Pa, respectively. Following pupil dilation, the pressure difference increased in all cases. For the compressible iris model, the pressure increased by 4.70%, 63.75%, and 52.17% near the pupil, at the iris mid-periphery, and near the iris periphery, respectively. For the nearly incompressible model, the pressure increased by 7.06%, 51.25%, and 55.43% near the pupil, at the iris mid-periphery, and near the iris periphery, respectively. Across a 400-micron diameter hole, the pressure difference developed was extremely small (< 0.1 Pa) across all cases, both before and following dilation. Conclusion: While LPI offers a solution for narrow or closed anterior chamber angles, in some patient populations the angles remain occludable following LPI. One possible reason could be attributed to the additional pressure difference across the anterior and posterior chamber due to the change in LPI hole size following dilationinduced iris deformation. Our study shows that the LPI hole size/location affects the pressure difference in both compressible and nearly incompressible irides.